The invention relates to dissolving barium sulfate solids from locations in and around the boreholes of wells and/or other relatively remote locations into which a fluid can be flowed.
Various well treating procedures for removing various types of scales with aminopolyacetic acid salt chelating agents, such as EDTA (ethylenediaminetetraacetic acid), are known. For example, U.S. Pat. No. 2,396,938 (filed in 1944) described removing boiler scale with aqueous solutions of such a chelant and an alkali meta hydroxide. U.S. Pat. No. 2,802,788 (filed in 1952) describes a radiator cleaning composition in which such a chelant salt is included in a aqueous solution along with an inorganic chelant, e.g., sodium tripolyphosphate. U.S. Pat. No. 3,308,065 (filed in 1963) describes a substantially one-pore volume treatment for removing calcium sulfate-containing scale with an ammoniated or aminated chelant, e.g., an ammonium salt of EDTA. U.S. Pat. No. 3,660,287 (filed in 1967) describes a similar treatment for dissolving calcium sulfate-containing scale with a mixture of an EDTA salt and water soluble inorganic carbonate salt. Such prior processes were consistent in utilizing an amount of solution which about filled one pore volume of the region within which the scale was to be removed and using a concentration of chelant such that that volume of the solution contained a stoichiometric excess relative to the amount of scale to be dissolved. U.S. Pat. Nos. 2,877,848 and 4,030,548 relate to using relatively dilute solutions. The U.S. Pat. No. 4,030,548 describes the tendancy for relatively concentrated EDTA solutions to become quickly saturated with a Ba-EDTA complex and suggests a once-through-dynamic wash treatment with enough solution to gradually remove the solid.
Bicyclic macrocyclic polyethers and the barium sulfate dissolving capability of aqueous solutions containing them are disclosed in "Tetrahedron Letters" No. 34 (1969), pages 2889-2892. U.S. Pat. No. 3,966,766 contains an example of such a polyether and the naming and position numbering conventions relative to such compounds. That examples comprises 4, 7, 13, 16, 21, 24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (which is hereafter referred to as "Compound A"), of the formula: ##STR1##